Mother rabbits typically build a nest anytime from a few days before the birth up until the day of the birth. Rabbits do build nests but after they have made a nest do not sit on it like a chicken would. They also dont stay on or near the nest after the babies are born.
Female rabbits will begin to construct a nest only after they conceive. Though they have on which is used for sleeping, they will build another before they give birth. Don't worry if she does not show interest just yet as there is no real hurry. Nature will take its course.